On the electrical side, I would extremely highly recommend going all 24 volt. This is a much simpler system and there is less line drop/voltage drop on the longer runs. Almost everything is available in 24 volt. A few critical pumps you might want to buy a spare, but overall you would be way ahead to use only one voltage. Regarding the Scania, it measures 2.5" taller than the JD 6090, measured from the crankshaft center. Will the engine be a tight fit under the cabin sole, or will you have 4" or more of clearance? Will the cockpit floor be lower than the cabin sole?